1. Field of the Invention
This invention relates to a heat-sensitive stencil master sheet. Particularly it relates to a heat-sensitive stencil master sheet having superior perforating and printing characteristics, and a process for digital-perforating the heat-sensitive stencil master sheet using a digital stencil-making device having a thermal head.
2. Description of the Related Art
The stencil master sheet so far used for stencil master printing has generally been prepared by adhering a thermoplastic resin film (hereinafter often abbreviated to film) onto a permeable substrate with an adhesive. In recent years, as such a stencil master sheet, a heat-sensitive sheet for digital perforation by the heat of a thermal head is prevailing, and in order to obtain printed matters having good resolving properties, a heat-sensitive stencil-making and printing device having a thermal head having a high resolution is used. As conditions of the permeable substrate used for the heat-sensitive stencil master sheet, easy handling, no occurrence of wrinkles in the sheet at the time of perforation, durability to printing, etc. are required. Since the quantity of ink passed through the perforated master sheet for the printed image and its quantity retained in the master sheet vary depending upon the kind of the substrate, various regulations of the master sheet such as basis weight, thickness, density, dispersibility of ink, strength (or wet strength), stiffness, etc. have been provided.
However, the heat-sensitive stencil master sheet used in the prior art has been chosen based mainly upon the quantity of ink passed and the quantity of ink retained relative to the image properties, but no sufficient consideration has been paid to the effect upon the perforation of film, and there may occur a case of insufficient perforation or a case of connected perforations, where it is difficult to control the quantity of ink passed.
Printed matters printed by a perforated stencil master sheet having insufficient perforations or non-perforated parts have drawbacks in that they are inferior in the resolving properties and the reproduction of fine letters, to cause parts where no ink is attached, such as white points at a solid part or parts reduced in ink concentration. Further, printed matters printed by a perforated stencil master sheet having connected or broadened perforations have drawbacks in that the quantity of ink transferred increases extremely, and reduction in the resolving properties or increase in the setting-off of ink to the surface of the printed matter due to exudation of ink occur.